1. Field of the Invention
The present invention relates to a diecasting apparatus.
2. Description of the Prior Art
Usual diecasting apparatuses are generally classified into two kinds; a horizontal diecasting apparatus whose molten metal injecting system is substantially horizontally arranged for horizontally injecting molten metal into dies and a vertical diecasting apparatus whose injecting system is substantially vertically arranged for vertically injecting molten metal into dies. The former has disadvantages in that in a pouring step a molten metal at a high temperature spreads at the bottom of an injection cylinder and remains thereat for a relatively long period of time, so that the molten metal tends to cool rapidly during the time from pouring to injecting and also tends to entrain air into a cavity when being injected. It is therefore difficult for the horizontal diecasting apparatus to obtain high quality diecast products. On the other hand, with the vertical diecasting apparatus, although it is improved by having less areas in contact with the air, it has also disadvantages in that the pouring operation of molten metal into an injection cylinder is troublesome and the molten metal still tends to cool due to its staying in an injection cylinder for a long period of time.
As can be seen from the above description, the hitherto used diecasting methods have an important disadvantage of imposing on operators a process of pouring a molten metal into an injection cylinder from a melting shop, a maintaining furnace, a temperature keeping furnace or the like arranged near the diecasting apparatus by means of a ladle or other means. In this case, it is clear that prevention of the molten metal from cooling is impossible and a continuous handling of the molten metal with safety and security is difficult. Particularly, as the molten metal at a high temperature is poured with the aid of its head, problems of thermal cracks, welding of the molten metal or the like arise on the injection cylinder where the molten metal falls. This phenomenon is particularly acute in high melting point metals, which considerably shortens the life of the part against which the molten metal is poured. Moreover, with the high melting point metals including titanium, aluminum or the like the transferring and pouring of the molten metals in the air greatly affects the quality of diecast products, so that high quality diecast products could not be obtained in the prior art.
In order to solve the above problems, it has been suggested to melt a high melting point metal immediately above a pouring gate of an injection cylinder and then pour it by falling. This method achieves a shortening of the time and distance for transferring the molten metal, but still gives rise to a thermal shock at the place where the molten metal falls, and the molten metal cools during the time from pouring to injection in the same manner as above described. On the other hand, it has been proposed to pour a molten metal from a warm keeping furnace into an injection cylinder by means of electromagnetic force or pneumatic pressure. This method requires to keep the passage of the molten metal warm sufficiently, and is difficult to obtain a fixed quantity of diecast products and an apparatus for this method is highly expensive and complicated and bulky in construction requiring a wide space for an installation.